My WindSock

This site, another from Ben Norbury (SpinLoose), can help you to anticipate the effect of wind on your chosen segment. The site is pitched at people taking part in competitive time trials, and could help to plan your strategy for the event, and perhaps influence your choice of wheels too.

The visualisation is very clear and it's simple to see where the headwinds/crossroads/tailwinds will be on your circuit.